<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        body,
        html {
            margin: 0 auto;
            padding: 0;
            height: 100%;
            width: 100%;
        }

        #app {
            height: 100%;
            width: 100%;
        }

        * {
            box-sizing: border-box;
        }

        .loginMask {
            height: 100%;
            width: 100%;
            background-color: lightslategrey;
            opacity: 0.9;
            position: absolute;
            top: 0;
            left: 0;
            z-index: 100;
            display: flex;
            justify-content: center;
            align-items: center;
            font-size: 50px;
            color: white;
        }
    </style>
</head>

<body>
    <div id="app"></div>
</body>

</html>